The developments of various nanoparticles, also called nanocrystals, have been actively tried since they may be materials for a new emerging area known as nanotechnology in such applications areas as ultra-high density magnetic data storage media, biomedical labeling reagents, nanoscale electronics, the source materials for very highly efficient laser beams and very bright optical devices.
For such a wide range of applications, the method of synthesizing monodisperse nanoparticles with a size variation of less than 5% is a very important key factor in controlling the basic characteristics of the base materials, because the properties of these nanoparticles are strongly dependent upon the dimension of the nanoparticles.
For example, the determining factor for the color sharpness of the nanocrystal-based optical devices in a semiconductor is primarily the uniformity in the size of the nanoparticles, where such monodisperse magnetic nanoparticles are critical base material for the application to the ultra-high density magnetic storage media.
Since such monodisperse nanoparticles can be used for a wide range of applications as described above, it is highly desirable to develop a process for producing the base nanoparticle material in large quantity.
Unfortunately, the synthesis process for monodisperse nanoparticles which have been known until now, are limited to the sub-gram level of quantities.
Murray et al. disclosed in U.S. Pat. No. 6,262,129 B1 a method of synthesizing nanoparticles of transition metals from the reaction of metal precursors at high temperature, in which method the size selection procedure for achieving a size uniformity required certainly for controlling the desired characteristics, is a high cost and difficult process for mass producing the monodisperse nanoparticles, whereby the large scale production of the base material is hampered in this method.
Monodisperse gold nanoparticles have been synthesized by the digestive ripening of the initially polydisperse nanoparticles[Stoeva, S. et al., “Gram-Scale Synthesis of Monodisperse Gold Colloids by the Solvated Metal Atom Dispersion Method and Digestive Ripening and Their Organization into Two- and Three-Dimensional Structures”, J. Am. Chem. Soc. 2002, 124, 2305].
However, long aging time as well as the difficulty in size uniformity control are deterring factors for the large scale synthesis of monodisperse gold nanoparticles.
Hyeon, T. et al. disclosed a synthesis method, without a size selection process, of monodisperse magnetic iron oxide nanoparticles from the thermal decomposition of iron-oleate complex prepared from the reaction of iron pentacarbonyl and oleic acid [Hyeon, T. et al., “Synthesis of Highly-Crystalline and Monodisperse Maghemite Nanocrystallites without a Size-Selection Process,” J. Am. Chem. Soc. 2001, 123, 12798]. However, iron pentacarbonyl used as a precursor, is extremely toxic and the method is not suitable for the large scale production of monodisperse nanoparticles.
Puntes, V. et al. reported on the synthesis method of monodisperse cobalt nanoparticles from the thermal decomposition of dicobalt octacarbonyl[CO2(CO)8] in the presence of surfactants[Puntes, V. F. et al., “Colloidal Nanocrystal Shape and Size Control: The Case of Cobalt”, Science 2001, 291, 2115]. However, use of expensive and highly toxic dicobalt octacarbonyl is a detrimental factor for synthesizing monodisperse nanoparticles in large quantity.
Sun, S. et al. reported on the synthesis of monodisperse nanoparticles of metal ferrites [MFe2O4, where M=Fe, Co or Mn] from the thermal decomposition of a mixture of metal acetates in the presence of oleic acid and oleylamine [Sun, S. et al., “Monodisperse MFe2O4 (M=Fe, Co, Mn) Nanoparticles”, J. Am. Chem. Soc. 2004, 126, 273; Sun, S. et al., “Size-Controlled Synthesis of Magnetite Nanoparticles”, J. Am. Chem. Soc. 2002, 124, 8204]. The use of expensive metal acetates prevents from synthesizing monodisperse nanoparticles in large quantity.
Jana, N. et al. disclosed a simple and generalized reaction system for synthesizing metal oxide nanoparticles through the pyrolysis of metal fatty acid salts [Jana, N. et al., “Size- and Shape-Controlled Magnetic (Cr, Mn, Fe, Co, Ni) Oxide Nanoparticles via a Simple and General Approach”, Chem. Mater. 2004, 16, 3931].
Although this synthetic approach has some advantages over the prior arts cited above in that relatively safe and inexpensive metal fatty acid salts are employed, this method has a drawback of vary difficult and time consuming neutralization and purification steps to process through by employing one pot reaction from a mixture of metal salt, fatty acid and NaOH in order to obtain the metal fatty acid salts, thereby such drawback makes it difficult to synthesize the monodisperse nanoparticles in large quantity.
Also, Yu, W. et al. reported a method of producing monodisperse magnetite nanoparticles from the thermal decomposition of metal fatty acid salts using a very similar method as Jana, et al. described above [Yu, W. et al., “Synthesis of Monodisperse Iron Oxide Nanoparticles by Thermal Decomposition of Iron Carboxylate Salts”, Chem. Comm. 2004, 2306].
In order to overcome the deficiencies of the prior arts, the present inventors had studied a novel process for synthesizing monodisperse nanoparticles in large quantity using inexpensive and non-toxic metal salts as reactants, where the process is suitable for synthesizing monodisperse nanoparticles in quantity of as much as 100 grams in a single reaction using 500 mL of solvent without a size selection process, and moreover, the size of the monodisperse nanoparticle is controlled simply by altering the synthesis conditions.
The present inventors have come to the completion of a novel process for making the monodisperse nanoparticles of various transition metals, metal alloys, metal oxides, and multimetallic oxides and its variations.
Therefore, the primary object of the present invention is to provide a novel process for making monodisperse nanoparticles of metals, metal alloys, metal oxides and multi-metallic oxides in large quantity from inexpensive and non-toxic metal salts without size-selection process.